1. Field of the Invention
The present invention relates to an apparatus for automatically engraving mimeographic papers, by which the displays of black color and any other colors on the original are independently decomposed into two colors and are read out, to engrave two types of stencil papers.
2. Description of the Prior Art
Conventional apparatus for automatically engraving a mimeographic stencil paper had been designed mainly for making a stencil paper for a single-color mimeographic printing for use with originals which bear only black color characters. Recently, however, the popularized colored printings have been making increased demands for the development of an automatic engraving machine which is capable of producing a variety of colors even in mimeographic printing.
The automatic engraving machines which are now commercially available and which are capable of effecting multi-color printing, have been provided with a rotary color filter plate in front of a light-receiving element faced to the original such that the rotating filter plate decomposes the colored display on the original into three colors, i.e., red, blue and yellow, to thereby prepare stencil papers for each of these colors. Therefore, the conventional automatic engraving machines were considerably complex in construction, difficult to manipulate and were expensive.
Another method consists of providing two automatic engraving machines, attaching filters of dissimilar colors to the light-receiving elements of each of the engraving machines, and separating the displays of the original, depending upon the colors, to prepare stencil papers by the separate engraving machines. In this case, however, since the originals and stencil papers are wound on the drums of separate engraving machines, it is difficult to bring their positions into agreement. Thus, a deviation is developed when the original is set to engrave the stencil paper, thereby making it difficult to obtain good colored printings. Further, the use of two automatic engraving machines requires considerable expense as well as clumsy operation for handling the engraving machines.
There has also been proposed a method of using a single automatic engraving machine. In this case, however, filters of different colors must be used for engraving the displays of the original depending upon the colors. In other words, the color filter attached to the light-receiving element must be replaced for each color of the display on the original, again resulting in clumsy operation.
In particular, in effecting the colored printing, it is highly desirable to develop an engraving machine which is capable of performing simple printings of two colors, such as black and red, which are often found in leaflets folded into the newspapers.